1. Field of the Invention
The invention relates to fuel injection devices for internal combustion engines; it is particularly suitable for use in so-called "multipoint" injection systems, in which each combustion chamber of the engine is provided with an injection device which has its outlet in the vicinity of a respective inlet valve.
In such a system, the nose of the injector is placed close to the combustion chamber of the engine which tends to heat it to a high temperature, which results in the nose being clogged up by the products or additives contained in the fuel delivered by the injector.
2. Prior Art
An injection device disclosed in U.S. Pat. No. 4,434,766 (Matsuoka et al) comprises an electrically controlled injector having a body provided with means for removably connecting said body in a passage opening into an engine induction passage and formed with a nose of reduced diameter and a cap fitted on the nose of the injector, formed with a fuel jet outlet opening, said cap being connected on the nose of the injector in such a position that it defines an air chamber with said nose and is formed with lateral openings communicating the air chamber with a space formed between the cap and the wall of said passage, said space being for connection to an air source.
As described, the outlet of the passage in the injector nose is connected to an air source.
It is further known to compensate for the direct air supply through a passage in an injector by giving to the minimum opening of the air intake butterfly valve a value which is slightly less than that which would be adopted in the absence of air delivery to the injectors.
A drawback of the arrangement described in U.S. No. 4,434,766 is that it does not accurately and reproducibly define the size of the air chamber, unless expensive machining methods are used.